Sandwich electrodes and methods of making the same

ABSTRACT

In some embodiments, an electrode can include a first and second conductive layer. At least one of the first and second conductive layers can include porosity configured to allow electrolyte to flow therethrough. The electrode can also include an electrochemically active layer having electrochemically active material sandwiched between the first and second conductive layers. The electrochemically active layer can be in electrical communication with the first and second conductive layers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/596,019, filed Dec. 7, 2017. The entirety of the above referencedapplication is hereby incorporated by reference.

BACKGROUND Field

The present disclosure relates to electrochemical cells and electrodesused in electrochemical cells. In particular, the present disclosurerelates to sandwich electrodes and sandwich electrodes used inelectrochemical cells. The electrodes and electrochemical cells caninclude silicon and carbon composite materials for use in batteries,such as lithium ion batteries.

Description of the Related Art

A lithium ion battery typically includes a separator and/or electrolytebetween an anode and a cathode. In one class of batteries, theseparator, cathode and anode materials are individually formed intosheets or films. Sheets of the cathode, separator and anode aresubsequently stacked or rolled with the separator separating the cathodeand anode (e.g., electrodes) to form the battery. For the cathode,separator and anode to be rolled, each sheet must be sufficientlydeformable or flexible to be rolled without failures, such as cracks,brakes, mechanical failures, etc. Typical electrodes includeelectro-chemically active material layers on electrically conductivemetals (e.g., aluminum and copper). For example, carbon can be depositedonto a current collector along with an inactive binder material. Carbonis often used because it has excellent electrochemical properties and isalso electrically conductive. Electrodes can be rolled or cut intopieces which are then layered into stacks. The stacks are of alternatingelectro-chemically active materials with the separator between them.

SUMMARY

Example electrodes are provided. The electrode can comprise a firstconductive layer, a second conductive layer, and an electrochemicallyactive layer. At least one of the first and second conductive layers caninclude porosity configured to allow an electrolyte to flowtherethrough. The electrochemically active layer can includeelectrochemically active material sandwiched between the first andsecond conductive layers. The electrochemically active layer can be inelectrical communication with the first and second conductive layers.

In various electrodes, the at least one of the first and secondconductive layers can comprise foam, mesh, or perforated material. Atleast one of the first and second conductive layers can comprise metal.In some examples, at least one of the first and second conductive layerscan comprise nickel foam or a perforated copper foil. In some examples,at least one of the first and second conductive layers can comprisecarbon. In some instances, the at least one of the first and secondconductive layers comprises both the first and second conductive layers.

In some electrodes, the electrochemically active layer can comprisesilicon, germanium, tin, oxide, graphite, or a combination thereof. Insome instances, the electrochemically active layer can comprise a film.For example, the film can comprise a silicon carbon composite film. Insome instances, the electrochemically active layer can comprise at leastabout 50% to about 99% by weight of silicon. For example, theelectrochemically active layer can comprise the silicon at about 60% toabout 99% by weight, at about 70% to about 99% by weight, or at about80% to about 99% by weight.

Some electrodes can further comprise an attachment substance between theelectrochemically active layer and the first and/or second conductivelayer. For example, the attachment substance can include polyamideimide,polyimide resin, polyacrylic acid, or a combination thereof.

Some electrodes can further comprise a third conductive layer and asecond electrochemically active layer comprising electrochemicallyactive material. The second electrochemically active layer can besandwiched between the third conductive layer and the first or secondconductive layer. In some instances, the electrochemically active layerand the second electrochemically active layer can comprise the sameelectrochemically active material. In various embodiments, the electrodecan be a negative electrode.

Example electrochemical cells are also provided. The electrochemicalcell can comprise any one of the example electrodes. The electrochemicalcell can comprise a lithium ion battery.

Example methods of forming an electrode are provided. The method cancomprise sandwiching at least one electrochemically active layercomprising electrochemically active material between a first conductivelayer and a second conductive layer. At least one of the first andsecond conductive layers can include porosity configured to allowelectrolyte to flow therethrough. The method can also comprise adheringthe at least one electrochemically active layer to the first and secondconductive layers such that the at least one electrochemically activelayer is in electrical communication with the first and secondconductive layers.

Some methods can further comprise providing the first conductive layerwith the at least one electrochemically active layer. The firstconductive layer can be disposed on a first side of the at least oneelectrochemically active layer. Sandwiching can comprise disposing thesecond conductive layer on a second side of the at least oneelectrochemically active layer.

Some methods can further comprise providing the first conductive layerwhere a first electrochemically active layer can be provided with thefirst conductive layer, and providing the second conductive layer wherea second electrochemically active layer can be provided with the secondconductive layer. Adhering can comprise adhering the first and secondelectrochemically active layers to form the at least oneelectrochemically active layer sandwiched between the first and secondconductive layers. In some instances, the first and secondelectrochemically active layers can form a single electrochemicallyactive layer.

In some methods, adhering can comprise providing an adhesive layerbetween the at least one electrochemically active layer and the firstand/or second conductive layer. In some methods, adhering can compriseapplying pressure to the at least one electrochemically active layer toadhere the at least one electrochemically active layer to the first andsecond conductive layers. In some methods, adhering can compriseapplying heat to the at least one electrochemically active layer toadhere the at least one electrochemically active layer to the first andsecond conductive layers.

Some methods can further comprise punching the first conductive layer,the second conductive layer, and the at least one electrochemicallyactive layer. In some instances, the method can further compriseapplying heat to the at least one electrochemically active layer tosinter the at least one electrochemically active layer to the first andsecond conductive layers.

Some methods can further comprise sandwiching at least one secondelectrochemically active layer comprising electrochemically activematerial between a third conductive layer and the first or secondconductive layer, and adhering the at least one second electrochemicallyactive layer to the third conductive layer and the first or secondconductive layer such that the at least one second electrochemicallyactive layer can be in electrical communication with the thirdconductive layer and the first or second conductive layer. In someinstances, adhering the at least one electrochemically active layer andadhering the at least one second electrochemically active layer canoccur simultaneously.

In some methods, the at least one of the first and second conductivelayers can comprise foam, mesh, or perforated material. In someinstances, at least one of the first and second conductive layers cancomprise metal. In some instances, at least one of the first and secondconductive layers can comprise carbon.

In some methods, the at least one electrochemically active layer cancomprise silicon, germanium, tin, oxide, graphite, or a combinationthereof. In some instances, the at least one electrochemically activelayer can comprise a silicon carbon composite film. In some instances,the electrochemically active layer can comprise at least about 50% toabout 99% by weight of silicon. In some examples, the electrode can be anegative electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates an example electrode in accordance withcertain embodiments described herein.

FIGS. 2a and 2b schematically illustrate additional example electrodesin accordance with certain embodiments described herein.

FIG. 3 illustrates an example method of forming an electrode inaccordance with certain embodiments described herein.

FIG. 4 illustrates another example method of forming an electrode inaccordance with certain embodiments described herein.

FIGS. 5a and 5b show an example sandwich electrode made in accordancewith certain embodiments described herein.

FIG. 6a schematically illustrates a cross sectional view of a sandwichelectrode in accordance with certain embodiments described herein.

FIG. 6b is a Scanning Electron Microscopy (SEM) image showing the crosssection of an example sandwich electrode.

FIG. 6c is a photograph of a top view of a punched sandwich electrode.

FIGS. 6d and 6e are SEM images showing the hole distribution in aperforated copper foil.

FIG. 6f is an SEM image showing Si/C composite film exposed through ahole of a perforated copper foil.

FIG. 7a is a photograph showing Si/C composite film adhering to theperforated copper foil.

FIG. 7b is an SEM image showing the electrode film partially transferredto the perforated copper foil.

FIG. 8a shows half cell test results of an example sandwich electrodeand a control electrode.

FIG. 8b shows the Coulombic efficiency of the example sandwichelectrode.

FIG. 9 shows the capacity retention of a cycled full cell having anexample electrode as described herein.

FIGS. 10a and 10b are SEM images of the control electrode and sandwichelectrode respectively after cycling.

DETAILED DESCRIPTION

Certain embodiments of electrodes (e.g., anodes and cathodes) andelectrochemical cells are described. The electrodes and electrochemicalcells can include a composite material comprising electrochemicallyactive material. In some embodiments, the composite material may includecarbonized polymer and silicon material. For example, a mixture thatincludes a carbon precursor and a silicon material can be formed into acomposite material. This mixture can include both carbon and silicon andthus can be referred to as a carbon-silicon composite material, asilicon-carbon composite material, a carbon composite material, or asilicon composite material.

Typical carbon anode electrodes include a current collector such as acopper sheet. Carbon is deposited onto the collector along with aninactive binder material. Carbon is often used because it has excellentelectrochemical properties and is also electrically conductive. Anodeelectrodes used in the rechargeable lithium-ion cells typically have aspecific capacity of approximately 200 milliamp hours per gram(including the metal foil current collector, conductive additives, andbinder material). Graphite, the active material used in most lithium ionbattery anodes, has a theoretical specific capacity of 372 milliamphours per gram (mAh/g). In comparison, silicon has a high theoreticalcapacity of 4200 mAh/g. Silicon, however, swells in excess of 300% uponlithiation. Because of this expansion, anodes including silicon mayexpand/contract and lose electrical contact to the rest of the anode.Accordingly, batteries with silicon anodes exhibit more rapid capacityloss upon cycling than those batteries with graphite anodes. Therepeated expansion and contraction of silicon particles during chargeand discharge can lead to mechanical failure of the anode, includingdisconnection between silicon and carbon, silicon and currentcollectors, as well as the disconnection between silicon particles.Therefore, a silicon anode should be designed to be able to expand whilemaintaining good electrical contact with the rest of the electrode.

Currently in a typical electrode design, silicon containing anodes havefree surfaces that expand and shrink during cycling. Once the siliconparticles are pulverized, they can be isolated from the activelyfunctioning anode to become “dead.” In certain embodiments, the siliconparticles can be retained in the electrode by incorporating a conductivelayer with porosity. The conductive layer with porosity can allow bothelectron and ion transport in addition to mechanical confinement, e.g.,to mitigate pulverization of silicon particles. For example, certainembodiments can include an additional conductive layer to sandwich theelectrochemically active material. This can reduce (and/or prevent insome instances) material that cracks or pulverizes from losingelectrical contact to the current collector. In addition, by includingporosity, electrolyte can flow through a conductive skeleton.

FIG. 1 schematically illustrates an example electrode in accordance withcertain embodiments described herein. The electrode 100 can be used as anegative electrode (i.e., an anode), a positive electrode (i.e., acathode), or both. Various embodiments of the electrode 100 can be usedin an electrochemical cell. The electrode 100 can be used in eithersecondary batteries (e.g., rechargeable) or primary batteries (e.g.,non-rechargeable). The electrochemical cell can include a lithium ionbattery.

With continued reference to FIG. 1, the example electrode 100 caninclude a first conductive layer 110 and a second conductive layer 120.At least one of the first 110 and second 120 conductive layers caninclude porosity 125 configured to allow electrolyte to flowtherethrough (e.g., one or more pathways). The electrode 100 can alsoinclude an electrochemically active layer 130 comprisingelectrochemically active material sandwiched between the first 110 andsecond 120 conductive layers. The electrochemically active layer 130 canbe in electrically communication with the first 110 and second 120conductive layers. In various embodiments, a sandwich electrode 100 canbe formed such that the electrochemically active layer 130 is confinedbetween the first 110 and second 120 conductive layers, yet can allowelectrolyte to flow through the porosity 125 in the first 110 and/orsecond 120 conductive layer.

In some embodiments, the first conductive layer 110 and/or secondconductive layer 120 can act as a current collector. The firstconductive layer 110 and/or second conductive layer 120 can include anycurrent collector material known in the art or yet to be developed. Thefirst conductive layer 110 can include the same or different material asthe second conductive layer 120. In some embodiments, the firstconductive layer 110 and/or second conductive layer 120 can include ametal. Example metals include, but are not limited to, copper, nickel,iron, titanium, molybdenum, stainless steel, chromium, aluminum, or acombination thereof. In some instances, copper and/or nickel can be usedfor an anode, and aluminum can be used for a cathode. In someembodiments, the first 110 and/or second 120 conductive layer caninclude non-metallic materials. An example non-metallic conductivematerial includes carbon, indium tin oxide (ITO), silicon carbide, or acombination thereof.

The first conductive layer 110 and/or second conductive layer 120 canhave two sides (e.g., two opposite major surfaces) and a thicknesstherebetween. For example, the first conductive layer 110 can have afirst side 111, a second side 112, and a thickness 113. Likewise, thesecond conductive layer 120 can have a first side 121, a second side122, and a thickness 123. The shape and/or size of the first conductivelayer 110 can be the same as or different from the shape and/or size ofthe second conductive layer 120. For example, the length of the firstside 111 and/or second side 112 of the first conductive layer 110 can bethe same as or different from the length of the first side 121 and/orsecond side 122 of the second conductive layer 120. As another example,the thickness 113 of the first conductive layer 110 can be the same asor different from the thickness 123 of the second conductive layer 120.In some embodiments, the first conductive layer 110 and/or secondconductive layer 120 can include a sheet or foil.

In FIG. 1, the second conductive layer 120 is illustrated as havingporosity 125 such that the second conductive layer 120 can be anelectrolyte-penetrable conductive layer. For simplicity, porosity 125 isdescribed herein in terms of the second conductive layer 120. However,it is appreciated that in some instances, the first conductive layer 110can have porosity such that the first conductive layer 110 can be anelectrolyte-penetrable conductive layer instead of or in addition to thesecond conductive layer 120. In some embodiments, the first conductivelayer 110 and second conductive layer 120 can include porosity and canact as a current collector such that no other conductive layers may beneeded. For example, the electrochemically active material layer canhave an electrolyte-penetrable conductive layer on one side and anotherelectrolyte-penetrable conductive layer on the other side of the activematerial layer.

In various embodiments, the porosity 125 can include one or morepathways that begin at the first side 121 and end at the second side 122of the conductive layer 120 (e.g., providing a passage for electrolyteto flow through the conductive layer 120). In some instances, theporosity 125 can include a direct path, while in some other instances,the porosity 125 can include a tortuous path. At least one pathway ofthe porosity 125 can extend through the thickness 123 of the conductivelayer 120. In some examples, at least one pathway of the porosity 125can have a length substantially equal to the thickness 123 of theconductive layer 120. In some examples, at least one pathway of theporosity 125 can have a length greater than the thickness 123 of theconductive layer 120.

The size, shape, and frequency of the porosity 125 is not particularlylimited but can be sized, shaped, and spaced apart to allow sufficientelectrolyte to flow therethrough, yet not allow the active particles toflow therethrough. In some instances, the porosity 125 can be spacedapart from other porosity 125 by about 1 mm or less, or in a range fromabout 0.1 mm to about 1 mm (e.g., about 0.1 mm, about 0.2 mm, about 0.3mm, about 0.4 mm, about 0.5 mm, about 0.6 mm, about 0.7 mm, about 0.75mm, about 0.8 mm, about 0.9 mm, or about 1 mm), or in a range withinthis range such as any range formed by the example values (e.g., fromabout 0.2 mm to about 1 mm, from about 0.3 mm to about 1 mm, from about0.5 mm to about 1 mm, from about 0.1 mm to about 0.9 mm, from about 0.2mm to about 0.9 mm, from about 0.5 mm to about 0.9 mm, from about 0.1 mmto about 0.8 mm, from about 0.2 mm to about 0.8 mm, from about 0.5 mm toabout 0.8 mm, from about 0.1 mm to about 0.75 mm, from about 0.2 mm toabout 0.75 mm, from about 0.5 mm to about 0.75 mm, from about 0.1 mm toabout 0.5 mm, from about 0.2 mm to about 0.5 mm, etc.). In someinstances, the size of the porosity 125 can be smaller than the size ofthe active material. In some embodiments, the average porosity size (orthe average diameter or the average largest dimension) or the medianporosity size (or the median diameter or the median largest dimension)can be less than about 50 μm, less than about 40 μm, less than about 30μm, less than about 20 μm, less than about 10 μm, less than about 1 μm,between about 10 nm and about 50 μm, between about 10 nm and about 40μm, between about 10 nm and about 30 μm, between about 10 nm and about20 μm, between about 0.1 μm and about 20 μm, between about 0.5 μm andabout 20 μm, between about 1 μm and about 20 μm, between about 1 μm andabout 15 μm, between about 1 μm and about 10 μm, between about 10 nm andabout 10 μm, between about 10 nm and about 1 μm, less than about 500 nm,less than about 100 nm, and about 100 nm. In some embodiments, theporosity 125 can be formed by one or more pores or interconnected poresin the conductive layer 120.

In various embodiments, the first conductive layer 110 and/or secondconductive layer 120 can include foam, mesh (e.g., woven or non-woven),or perforated material. As an example, the first conductive layer 110and/or second conductive layer 120 can include nickel foam. As anotherexample, the first conductive layer 110 and/or second conductive layer120 can include a perforated copper foil. As another example, the firstconductive layer 110 and/or second conductive layer 120 can includecarbon foam, carbon mesh, porous carbon, perforated carbon film, etc.

With continued reference to FIG. 1, the electrochemically active layer130 sandwiched between the first conductive layer 110 and secondconductive layer 120 can be in electrically communication with the firstconductive layer 110 and second conductive layer 120. For example, theelectrochemically active layer 130 can have a first side 131 and asecond side 132. The first side 131 of the electrochemically activelayer 130 can be positioned adjacent the second side 112 of the firstconductive layer 110. The second side 132 of the electrochemicallyactive layer 130 can be positioned adjacent the first side 121 of thesecond conductive layer 120.

The electrochemically active layer 130 can include electrochemicallyactive material. The electrochemically active material can include anyelectrochemically active material. For example, the electrochemicallyactive material can include silicon, germanium, tin, oxide, graphite, ora combination thereof. As additional examples, the electrochemicallyactive material can include higher-voltage active materials such aslithium cobalt oxide, lithium cobalt aluminum oxide, various forms oflithium nickel manganese cobalt oxide (NMC), various forms of lithiummanganese oxide (LMO), etc. As described herein, various embodiments caninclude a silicon-carbon (or carbon-silicon) composite material. U.S.patent application Ser. No. 13/008,800, filed Jan. 18, 2011, andpublished on Jul. 21, 2011 as U.S. Patent Application Publication No.2011/0177393, entitled “Composite Materials for ElectrochemicalStorage;” U.S. patent application Ser. No. 13/601,976, filed Aug. 31,2012, and published on Jun. 19, 2014 as U.S. Patent ApplicationPublication No. 2014/0170498, entitled “Silicon Particles for BatteryElectrodes;” and U.S. patent application Ser. No. 13/799,405, filed Mar.13, 2013, and published on Jun. 19, 2014 as U.S. Patent ApplicationPublication No. 2014/0166939, entitled “Silicon Particles for BatteryElectrodes,” each of which is incorporated by reference herein, describecertain embodiments of carbon-silicon composite materials usingcarbonized polymer and silicon material. In various embodiments, theelectrochemically active layer 130 can include a film, e.g., asilicon-carbon composite film.

In some embodiments, the electrochemically active layer 130 can includefrom greater than 0% to about 99% by weight of electrochemically activematerial. For example, the amount of electrochemically active materialby weight of the electrochemically active layer 130 can include anyweight percent within this range (e.g., about 10%, about 15%, about 20%,about 25%, about 30%, about 35%, about 40%, about 45%, about 50%, about55%, about 60%, about 65%, about 70%, about 75%, about 80%, about 85%,about 90%, about 95%, about 96%, about 97%, about 98%, about 99%, etc.),or any range within this range such as any range formed by the examplevalues (e.g., greater than about 0% to about 25% by weight, greater thanabout 0% to about 35% by weight, greater than about 0% to about 50% byweight, greater than about 0% to about 70% by weight, greater than about0% to about 90% by weight, greater than about 0% to about 95% by weight,from about 10% to about 35% by weight, from about 10% to about 50% byweight, from about 10% to about 90% by weight, from about 10% to about95% by weight, from about 10% to about 99% by weight, from about 30% toabout 85% by weight, from about 30% to about 90% by weight, from about30% to about 95% by weight, from about 30% to about 99% by weight, fromabout 50% to about 85% by weight, from about 50% to about 90% by weight,from about 50% to about 95% by weight, from about 50% to about 99% byweight, from about 60% to about 85% by weight, from about 60% to about90% by weight, from about 60% to about 95% by weight, from about 60% toabout 99% by weight, from about 70% to about 85% by weight, from about70% to about 90% by weight, from about 70% to about 95% by weight, fromabout 70% to about 99% by weight, from about 80% to about 90% by weight,from about 80% to about 95% by weight, from about 80% to about 99% byweight, etc.).

In some embodiments, the electrode 100 can include an attachmentsubstance (not shown) between the electrochemically active layer 130 andthe first 110 and/or second 120 conductive layer. An attachment (e.g.,adhesive) substance can be used to couple or adhere theelectrochemically active layer 130 to the first 110 and/or second 120conductive layer (e.g., to prevent delamination between them).

The attachment substance can include any attachment substance such as anattachment substance as described in U.S. patent application Ser. No.13/333,864, filed Dec. 21, 2011, and published on Jun. 19, 2014 as U.S.Patent Application Publication No. 2014/0170482, entitled “Electrodes,Electrochemical Cells, and Methods of Forming Electrodes andElectrochemical Cells,” or U.S. patent application Ser. No. 13/796,922,filed Mar. 12, 2013, and published on Jun. 19, 2014 as U.S. PatentApplication Publication No. 2014/0170475, entitled “Electrodes,Electrochemical Cells, and Methods of Forming Electrodes andElectrochemical Cells,” each of which is incorporated by referenceherein. In some embodiments, the attachment substance can besubstantially electrically nonconductive (e.g., the attachment substancehas an electrically conductivity such that, in use of the adhesivesubstance in an electrochemical cell, the attachment substance does notconduct electricity). In some instances, portions of theelectrochemically active layer 130 may penetrate the layer of attachmentsubstance and come in direct contact (e.g., physical contact) with thefirst 110 and/or second 120 conductive layer (e.g., allowing electronsto travel directly from the electrochemically active layer 130 to thefirst 110 and/or second 120 conductive layer).

The attachment substance may be a polymer. In certain embodiments, theattachment substance includes polyamideimide (PAI) or is PAI. In someembodiments, the attachment substance includes polyimide resin or ispolyimide resin. In further embodiments, the attachment substanceincludes polyvinylidene fluoride (PVDF) or is PVDF, includescarboxymethyl cellulose (CMC) or is CMC, or includes polyacrylic acid(PAA) or is PAA. The attachment substance may also be other materialsthat provide sufficient adhesion (e.g., bonding strength) to bothelectrochemically active layer 130 and the first 110 and/or second 120conductive layer. Additional examples of chemicals that can be or beincluded in the attachment substance include styrene butadiene rubber(SBR), polypyrrole (PPy), poly(vinylidenefluoride)-tetrafluoroethylene-propylene (PVDF-TFE-P), polyacrylonitrile,polytetrafluoroethylene, polyhexafluoropropylene, polyethylene oxide,polypropylene oxide, polyphosphazene, polysiloxane, polyvinyl fluoride,polyvinyl acetate, polyvinyl alcohol, polymethylmethacrylate,polymethacrylic acid, nitrile-butadiene rubber, polystyrene,polycarbonate, and a copolymer of vinylidene fluoride and hexafluoropropylene. The attachment substance may be a thermoset polymer or athermoplastic polymer, and the polymer may be amorphous,semi-crystalline, or crystalline.

FIGS. 2a and 2b schematically illustrate additional example electrodesin accordance with certain embodiments described herein. In FIG. 2a ,the example electrode 100 a includes a third conductive layer 140 a anda second electrochemically active layer 135 a. The third conductivelayer 140 a is positioned such that the second electrochemically activelayer 135 a is sandwiched between the third conductive layer 140 a andsecond conductive layer 120 a. In FIG. 2b , the third conductive layer140 b is positioned such that the second electrochemically active layer135 b is sandwiched between the third conductive layer 140 b and firstconductive layers 110 b. The third conductive layer 140 a, 140 b may ormay not include porosity 145 a, 145 b to allow electrolyte to flowtherethrough. For example, the third conductive layer 140 a, 140 b mayor may not include porosity 145 a, 145 b, e.g., depending on whether thesecond conductive layer 120 a and/or first conductive layer 110 b hasporosity. In various embodiments, one, two, or all three of theconductive layers can have porosity configured to allow electrolyte toflow therethrough.

It is appreciated that the third conductive layer 140 a, 140 b mayinclude the same or different material as the first 110 a, 110 b and/orsecond 120 a, 120 b conductive layer. In addition, the secondelectrochemically active layer 135 a, 135 b may include the same ordifferent material as the first electrochemically active layer 130 a,130 b. For example, the second electrochemically active layer 135 a, 135b may include the same or different electrochemically active material asthe first electrochemically active layer 130 a, 130 b. Furthermore, someelectrodes can include additional conductive layers (e.g., four, five,six, etc.) and/or additional electrochemically active layers (e.g.,three, four, five, six, etc.).

FIG. 3 illustrates an example method of forming an electrode (e.g., theelectrode 100 schematically illustrated in FIG. 1). As shown in block310, the method 300 of forming an electrode can include sandwiching atleast one electrochemically active layer between first and secondconductive layers. The electrochemically active layer can includeelectrochemically active material. At least one of the first and secondconductive layers can comprise porosity configured to allow electrolyteto flow therethrough.

As shown in block 320, the method 300 of forming an electrode caninclude adhering the electrochemically active layer to the first andsecond conductive layers, for example, such that the electrochemicallyactive layer is in electrical communication with the first and secondconductive layers.

With reference to block 310, one embodiment of the electrochemicallyactive layer may be, for example, the electrochemically active layer 130in FIG. 1. The electrochemically active layer can includeelectrochemically active material (e.g., any electrochemically activematerial described herein). The first and/or second conductive layer caninclude any conductive layer described herein (e.g., first 110conductive layer and/or second conductive layer 120 in FIG. 1, etc.).The first and/or second conductive layer can include porosity 125configured to allow electrolyte to flow therethrough (e.g., porosity 125in FIG. 1).

With reference to FIG. 1, in some embodiments, the first conductivelayer 110 can be provided with the electrochemically active layer 130.For example, the first conductive layer 110 can be disposed on a firstside 131 of the electrochemically active layer 130. Sandwiching caninclude disposing the second conductive layer 120 on a second side 132of the electrochemically active layer 130. For example, in someembodiments, the electrochemically active layer can be coated on acurrent collector and an electrolyte-penetrable conductive layer can beadhered on the other side of the electrochemically active layer 130 toform the sandwich electrode.

In some embodiments, two layers of electrolyte-penetrable conductivelayers can surround an electrochemically active layer. Theelectrolyte-penetrable conductive layers can act as current collectorssuch that no other conductive layer may be needed. In some suchembodiments, the electrochemically active layer can be coated on anelectrolyte-penetrable layer, and another electrolyte-penetrable layercan be adhered on the other side.

In some embodiments, the first 110 and second 120 conductive layers canbe provided with a first and second electrochemically active materialrespectively. The method 300 of forming can include adhering the firstand second electrochemically active material together to form theelectrochemically active layer 130 sandwiched between the first 110 andsecond 120 conductively layers. In some instances, the first and secondelectrochemically active material can form a single electrochemicallyactive layer 130.

In some embodiments, the electrochemically active layer 130 can beadhered to the first 110 and/or second 120 conductive layer by providingan adhesive layer (e.g., attachment substance) between theelectrochemically active layer 130 and the first 110 and/or second 120conductive layer.

The attachment substance can be applied between the electrochemicallyactive layer 130 and the first 110 and/or second 120 conductive layerusing any method known in the art or yet to be developed. For example,the attachment substance can be applied using a solution (e.g., a wetprocess) as described in U.S. patent application Ser. No. 13/333,864,filed Dec. 21, 2011, and published on Jun. 19, 2014 as U.S. PatentApplication Publication No. 2014/0170482, entitled “Electrodes,Electrochemical Cells, and Methods of Forming Electrodes andElectrochemical Cells,” which is incorporated by reference herein. Asanother example, the attachment substance can be applied using anattachment substance in a substantially solid state (e.g., asubstantially dry process) as described in U.S. patent application Ser.No. 13/796,922, filed Mar. 12, 2013, and published on Jun. 19, 2014 asU.S. Patent Application Publication No. 2014/0170475, entitled“Electrodes, Electrochemical Cells, and Methods of Forming Electrodesand Electrochemical Cells,” which is incorporated by reference herein.In various embodiments, the attachment substance does not block theporosity in the first 110 and/or second 120 conductive layers.

In some embodiments, additional adhesive materials can be used toimprove the adhesion between the layers. In some embodiments, theelectrochemically active layer 130 can be adhered to the firstconductive layer 110 and/or second conductive layer 120 throughmechanical adhesion.

In some examples, the electrochemically active layer 130 can be adheredto the first 110 conductive layer and/or second conductive layer 120 byapplying an appropriate pressure and/or heat (e.g., temperature) to theelectrochemically active layer 130. For example, a pressure from about10 MPa to about 50 MPa (e.g., any pressure within this range such asabout 10 MPa, about 15 MPa, about 20 MPa, about 25 MPa, about 30 MPa, 35MPa, 40 MPa, 45 MPa, 50 MPa, etc.), or any range within this range(e.g., any range formed by the example values such as about 10 MPa toabout 45 MPa, about 20 MPa to about 50 MPa, etc.) can be applied. Asanother example, a temperature from about 200° C. to about 350° C.(e.g., any temperature within this range such as about 200° C., about225° C., about 250° C., about 275° C., about 300° C., about 325° C.,about 350° C., etc.), or any range within this range (e.g., any rangeformed by the example values such as about 200° C. to about 325° C.,etc.) can be applied. In various embodiments, the applied temperaturecan be determined by the materials of any adhesives, theelectrochemically active layer 130, and/or the conductive layers 110,120. In some instances, applying heat can sinter the electrochemicallyactive layer to the first 110 and/or second 120 conductive layer.

In various embodiments, after the sandwich electrode is formed into asingle integrated piece, the electrode can be punched and processed.After the electrode is punched, the electrode can undergo heattreatment. In some embodiments, the heat treatment can enhance theadhesion between layers. For example, the punched sandwich electrodescan be annealed at high temperatures from about 500° C. to about 850° C.(e.g., any temperature within this range such as about 500° C., about525° C., about 550° C., about 575° C., about 600° C., about 625° C.,about 650° C., about 675° C., about 700° C., about 725° C., about 750°C., about 775° C., about 800° C., about 825° C., about 850° C., etc.) orany range within this range (e.g., any range formed by the examplevalues such as about 500° C. to about 825° C., about 500° C. to about800° C., etc.) to further sinter the layers together. In variousembodiments, the applied temperature can be determined by the materialsof the electrochemically active layer 130 and/or the conductive layers110, 120.

FIG. 4 illustrates another example method 400 of forming an electrode(e.g., the electrode 100 a, 100 b schematically illustrated in FIGS. 2aand 2b ). In some embodiments, the method 400 can include steps 410 and420, which can be similar to steps 310 and 320 in method 300.

Following such steps, as shown in block 430 in FIG. 4, the method 400 offorming can include sandwiching at least one second electrochemicallyactive layer between a third conductive layer and the first or secondconductive layer. With reference to FIG. 2a , the secondelectrochemically active layer 135 a can be sandwiched between the third140 a and second 120 a conductive layers. With reference to FIG. 2b ,the second electrochemically active layer 135 b can be sandwichedbetween the third 140 b and first 110 b conductive layers.

In various embodiments, as shown in block 440, the method 400 of formingcan include adhering at least one second electrochemically active layerto the third conductive layer and the first or second conductive layer,e.g., such that the second electrochemically active layer can be inelectrical communication with the third conductive layer and the firstor second conductive layer. With reference to FIG. 2a , the secondelectrochemically active layer 135 a can be adhered to the third 140 aand second 120 a conductive layers. The second electrochemically activelayer 135 a can be in electrical communication with the third 140 a andthe second 120 a conductive layers. With reference to FIG. 2b , thesecond electrochemically active layer 135 b can be adhered to the third140 b and first 110 b conductive layers. The second electrochemicallyactive layer 135 b can be in electrical communication with the third 140b and the first 110 b conductive layers.

In some embodiments, adhering the first electrochemically active layerand adhering the second electrochemically active layer can occursequentially. For example, with reference to FIG. 2a , in someembodiments, the first electrochemically active layer 130 a can beadhered to the first 110 a and second 110 b conductive layers.Subsequently, the second electrochemically active layer 135 a can beadhered to the third 140 a and second 120 a conductive layers.

In some embodiments, adhering the first electrochemically active layerand adhering the second electrochemically active layer can occursimultaneously. For example, with reference to FIG. 2b , in someembodiments, the first conductive layer 110 b can be coated with thefirst electrochemically active layer 130 b on one side and with thesecond electrochemically active layer 135 b on the other side. The firstelectrochemically active layer 130 b can be adhered to the firstconductive layer 110 b and second conductive layer 120 b at the sametime as the second electrochemically active layer 135 b is adhered tothe third conductive layer 140 b and first conductive layer 110 b. Otherexamples are possible.

EXAMPLES

The following examples are provided to demonstrate the benefits of someembodiments of electrodes, electrochemical cells, and methods of formingthe same. These examples are discussed for illustrative purposes andshould not be construed to limit the scope of the disclosed embodiments.

FIGS. 5a and 5b show an example sandwich anode made in accordance withcertain embodiments described herein. The sandwich anode was prepared bylaminating perforated copper foils onto a coated silicon-carboncomposite anode. For example, a silicon-carbon (Si/C) composite anodefilm was coated onto a copper foil current collector on both sides(e.g., a Si/C film sandwiching a copper current collector). The Si/Ccomposite films contained silicon particles and polyimide resin as abinder. The coated anode was then sandwiched by perforated copper foils(Yasunaga Corporation of Japan, high density PF0.1 and PF0.4 foils, with10 microns equivalent thickness), and laminated under pressure(approximately 20 MPa) and temperature (approximately 300° C.). Thepolyimide resin acted as a binder to attach the perforated copper foilsonto the surfaces of the coated Si/C anode. The perforated copper foilsand the original Si/C anode were integrated into a single piece afterlamination, punched, and processed. The punched sandwich anode wasannealed at a temperature of approximately 600° C. to sinter the layerstogether.

FIG. 6a-6f show the structure of a sandwich anode in accordance withcertain embodiments described herein, including the side and top views.For example, FIG. 6a schematically illustrates a cross sectional view ofan example sandwich anode. The sandwich anode includes two layers ofSi/C composite anode coating a copper current collector and sandwichedbetween two layers of perforated copper foils. The perforated copperfoils include holes for electrolyte to flow therethrough. FIG. 6b is aScanning Electron Microscopy (SEM) image showing the cross section of anexample sandwich anode. The SEM image shows that the top perforatedcopper foil can encapsulate the active Si/C anode films and thatelectrolyte can penetrate through the holes of the top perforated copperfoil. The cross section of the bottom perforated copper foil intersecteda region without holes, making the foil appear continuous and withoutholes. FIG. 6c shows a top view of the punched sandwich anode. The foilswere welded at the tabs to provide an electron path though the foils.FIGS. 6d and 6e are SEM images showing the hole distribution in theperforated copper foil. The black and white dashed lines show possiblepositions that intersect with and without holes, which lead to thedifferent cross sections viewed in FIG. 6b . For example, the perforatedcopper foil may appear to be continuous or with holes depending on thecutting position. FIG. 6f is an SEM image showing the Si/C film exposedthrough a hole of a perforated copper foil.

FIG. 7a is a photograph showing the gray Si/C film adhering to theperforated copper foil; and FIG. 7b is an SEM image showing the anodefilm partially transferred to the perforated copper foil, indicatinggood adhesion.

Half cells tests were performed on the example sandwich anode and acontrol anode without perforated copper foils. As shown in FIG. 8a ,cyclic voltammetry shows similar delithiation peaks in the first cyclefor the sandwich anode (solid line) and the control anode (dashed line),indicating that the electrochemistry is not altered by the extraperforated copper layers. FIG. 8b shows the Coulombic efficiency of thesandwich anode was more than 99% after 35 cycles and 99.4% after 80cycles (cycled at C/16 rate between 0.01V and 1.2V versus Li/Li+),indicating high reversibility of the sandwich anode.

The sandwich anode was also tested in a full cell. The sandwich anodewas coupled with a LiCoO₂ cathode and an electrolyte containing 1.2mol/L LiPF₆ salt in mixed solvents of fluoroethylene carbonate (FEC) andethyl methyl carbonate (EMC) with a ratio of FEC/EMC=3:7. FIG. 9 showsthat the capacity retention of the full cell cycled at 0.5 C between4.3V and 3.3V was greater than 80% at 200 cycles.

FIGS. 10a and 10b are SEM images of the control anode and sandwich anoderespectively after cycling. The morphology of the control anode showedsevere pulverization of active particles as some of the particles becamedangling on the surface. The morphology of the sandwich anode afterremoving the perforated copper foil had uniform and flat surfaceswithout significant pulverization.

As described herein, compared with other electrodes, electrodesincluding silicon may exhibit more rapid capacity loss upon cycling dueto relatively large volume changes. Certain embodiments described hereincan incorporate a conductive layer with porosity to significantlyimprove the performance of silicon anodes. Certain embodiments can alsobe used in other electrodes that may suffer from degradation due tolarge volume changes during cycling, including but not limited togermanium, tin, and oxide electrodes. Additional examples can alsoinclude higher-voltage active materials such as lithium cobalt oxide,lithium cobalt aluminum oxide, various forms of lithium nickel manganesecobalt oxide (NMC), various forms of lithium manganese oxide (LMO), etc.Various embodiments can also be extended to multiple metal or otherconductive layers in an electrode to provide enhanced mechanicalstrength and conductivity.

Various embodiments have been described above. Although the inventionhas been described with reference to these specific embodiments, thedescriptions are intended to be illustrative and are not intended to belimiting. Various modifications and applications may occur to thoseskilled in the art without departing from the true spirit and scope ofthe invention as defined in the appended claims.

What is claimed is:
 1. An electrode comprising: a first conductivelayer; a second conductive layer, at least one of the first and secondconductive layers comprising porosity configured to allow an electrolyteto flow therethrough; a first electrochemically active layer comprisingelectrochemically active material sandwiched between the first andsecond conductive layers, wherein the first electrochemically activelayer is in electrical communication with the first and secondconductive layers; a third conductive layer; and a secondelectrochemically active layer comprising electrochemically activematerial sandwiched between the third conductive layer and the first orsecond conductive layer.
 2. The electrode of claim 1, wherein the atleast one of the first and second conductive layers comprises foam,mesh, or perforated material.
 3. The electrode of claim 1, wherein theat least one of the first and second conductive layers comprises metal.4. The electrode of claim 1, wherein the at least one of the first andsecond conductive layers comprises nickel foam.
 5. The electrode ofclaim 1, wherein the at least one of the first and second conductivelayers comprises a perforated copper foil.
 6. The electrode of claim 1,wherein the at least one of the first and second conductive layerscomprises carbon.
 7. The electrode of claim 1, wherein the at least oneof the first and second conductive layers comprises both the first andsecond conductive layers.
 8. The electrode of claim 1, wherein the firstand/or second electrochemically active layer comprises silicon,germanium, tin, oxide, graphite, or a combination thereof.
 9. Theelectrode of claim 1, wherein the first and/or second electrochemicallyactive layer comprises a film.
 10. The electrode of claim 9, wherein thefilm comprises a silicon carbon composite film.
 11. The electrode ofclaim 1, wherein the first and/or second electrochemically active layercomprises at least about 50% to about 99% by weight of silicon.
 12. Theelectrode of claim 11, wherein the first and/or second electrochemicallyactive layer comprises the silicon at about 60% to about 99% by weight.13. The electrode of claim 12, wherein the first and/or secondelectrochemically active layer comprises the silicon at about 70% toabout 99% by weight.
 14. The electrode of claim 13, wherein the firstand/or second electrochemically active layer comprises the silicon atabout 80% to about 99% by weight.
 15. The electrode of claim 1, furthercomprising an attachment substance between the first and/or secondelectrochemically active layer and the first and/or second conductivelayer.
 16. The electrode of claim 15, wherein the attachment substancecomprises polyamideimide, polyimide resin, polyacrylic acid, or acombination thereof.
 17. The electrode of claim 1, wherein the firstelectrochemically active layer and the second electrochemically activelayer comprise the same electrochemically active material.
 18. Theelectrode of claim 1, wherein the electrode is a negative electrode. 19.An electrochemical cell comprising the electrode of claim
 1. 20. Theelectrochemical cell of claim 19, wherein the electrochemical cellcomprises a lithium ion battery.